The present invention relates to a method for manufacturing high quality fatty acid esters of lower alcohols useful as a starting material for the preparation of soaps, higher alcohols and the like. More particularly, the present invention relates to a method for manufacturing high quality fatty acid esters which can be processed into high-grade soap products without undertaking the treatment of salting-out as a means for purification hitherto considered to be indispensable in preparing soaps from fatty acid esters.
Lower alkyl esters of fatty acids such as methyl esters are widely used as a base material for the preparation of soaps and as a starting material for the synthesis of higher alcohols and certain kinds of surface active agents. They are manufactured industrially by the transesterification reaction of a fatty acid glyceride, i.e. oil or fat, and a lower alcohol, e.g. methyl alcohol. The industrial products of the lower alkyl esters of fatty acids manufactured in the above mentioned process naturally contain considerable amounts of colored or chromogenic impurities originating from the crude oil or fat as the starting material. Therefore, it is a usual practice that the crude soaps made from the esters are subjected to further purification by the method of salting-out since otherwise the quality of the finished soap bars obtained therefrom is very low.
Notwithstanding the industrially established process in which purification of the crude soaps by salting-out is almost always undertaken, such a purification treatment is preferably to be avoided because the procedure of salting-out requires very burdensome steps and extremely long time for aging when practiced in an industrial scale.
Generally speaking, there are known several methods for the purification of an organic substance such as lower alkyl esters of fatty acids to remove the colored or chromogenic impurities contained therein. They are, for example, a method of treatment with an alkali, a method of rectification distillation and a method of adsorption. These methods are not free from their respective drawbacks or problems. That is, the first method of alkali treatment has low efficiency and the yield of the purified products is impractically low. The method of rectification distillation is defective due to the consumption of relatively large quantity of heat energy and the yield of the purified products in the adsorption method is low due to the large loss of the material as remaining on the adsorbents. Thus, no satisfactory methods have yet been proposed for the mass production of fatty acid esters of high purity.